Many people carry PDAs, cellular phones, portable medical devices and so on with them all the time. To transmit data between these devices, a wired transmission method using cables and a wireless transmission method using radio waves and light are used.
The wired transmission method secures transmission data and has a high transmission rate but it has a shortcoming in that a user must carry a wired device such as a cable with him/her at all times. The wireless transmission method can easily transmit data but it requires additional circuits for wireless transmission and therefore it is difficult to reduce the cost of a communication device.
To solve the aforementioned problems, human body communication using the human body as a transmission medium has been recently proposed. That is, a signal output through a transmitter of a communication device is applied to the human body through an electrode connected to the human body and transmitted through the human body. The signal is received by a receiver of another communication device through another electrode connected to the human body. This human body communication is convenient to use because it does not need a wired device such as a cable and has an advantage in that it requires no additional circuits for wireless transmission.
Electrodes used for constructing a communication device for human body communication are divided into a signal electrode and a ground electrode based on their functions. The signal electrode is connected to an output signal line of a transmitter of the communication device or an input signal line of a receiver of the communication device in order to transmit a signal to the human body or to receive a signal from the human body. The ground electrode is connected to a grounding part of the communication device and affects the characteristics of signal transmission through the human body according to an arrangement direction of the signal electrode and the ground electrode and whether the ground electrode comes into contact with the human body.